1. Field of the Invention
This invention relates to the processing of workpieces with an energy beam and more particularly to creation of controlled inclined trenches and other microstructures in semiconductor wafers or polymer planar waveguides using a scanned laser.
2. Description of Related Art
Inclined surfaces in microstructures of semiconductor wafer substrates or polymer planar waveguides have been produced using image projection of stationary apertures of variable size, such that the aperture dimensions change while the laser is firing, or raster scanning a focused spot, increasing the number of scans toward the deep end of the ramp.
For example, U.S. Pat. No. 5,296,673 discloses an excimer laser projection system for ablation of a target material which has a lens system for projecting a mask pattern on the workpiece. The lens system is telecentric toward the target end of the projection path. The workpiece is moveable to define the area to be removed. In use the size of projected image area to be ablated from the target is adjusted substantially without altering the relative positions of the target.
U.S. Pat. No. 5,491,319, assigned to the assignee of the instant application, discloses a laser ablation apparatus and method in which a mechanism in the path of the beam shapes the cross-section of the beam and includes first and second linear actuators on opposite sides of the beam path which include a pluarity of linear members which are individually inserted and retracted into and out of the beam path to shape the beam. U.S. Pat. No. 4,940,508 discloses an excimer laser material removal system which includes an aperture structure having a plurality of openings of different size and shape and a stage movable in at least the X and Y directions.
U.S. Pat. No. 4,940,881 discloses control of the angles of the walls of the vias being ablated by an excimer laser by interposing refractive elements between the masks and the workpieces and rotating the refractive elements about axes parallel to the optical axis. The refractive element may have parallel faces or faces at an angle to each other.
The prior art does not easily control the inclination of angle and depth of the microstructures for application in photonic circuitry. Specifically, problems currently exist in the redirection of electromagnetic energy from the plane of circuitry to a direction out of the plane. When these structures are machined using laser energy, it has been found that the position of the beam spot (for raster-scan technique) or image dimensions (for variable-aperture technique) must be carefully controlled to produce repeatable results.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method and apparatus for controlling the angle and depth of inclined surfaces in microstructures by laser techniques.
It is another object of the present invention to provide a method and apparatus for creating controlled inclined surfaces by laser which utilizes available equipment.
It is a further object of the present invention to provide a reliable process for creation of inclined surfaces of controlled angle and depth of microstructures by excimer laser whose results may be interpreted through equations to establish desired parameters.